Biological, ecological and genetic aspects of Narrow leaved ash (Fraxinus angustifolia Vahl) in the northeastern Italy

Narrow leaved ash (Fraxinus angustifolia Vahl) is an important forest tree belonging to peculiar and threatened ecosystems, where it forms mixed populations with other deciduous trees. Its range partly overlaps with that of European ash (Fraxinus excelsior) and interspecific cross is possible. These habitats are of the utmost importance due to their high level of biodiversity, but highly threatened by human activities. Since climate change is expected to favor the diffusion of narrow leaved ash, a study was carried out with the aim of enhancing our knowledge of the biological, ecological and genetic aspects of this species. Twelve populations of narrow leaved ash from north-eastern Italy were sampled and their genetic variability was analyzed by means of six molecular markers (nuclear microsatellites), of which 4 gave consistent and repeatable results. Overall, 113 alleles were observed, of which 38 were present in only one population (private alleles). Consistent levels of genetic variability was found (mean number of alleles per locus = 7.08, effective number of alleles per locus = 4.37, expected heterozygosity = 0.613), though lower than those reported in the literature. Fixation index was very close to zero, indicating a good agreement with Hardy-Weinberg’s expectations. The genetic differentiation among populations was significant (both GST e FST as high as 0.102), although it was not possible to correlate the distribution of genetic variability with ecological or geographical factors. Genetic pools of F. excelsior and F. angustifolia were distinct, though several individuals showed intermediate genetic characteristics, especially in the population from Grotta di Farra where both species are present and many individuals showed intermediate morphological features. The presence of individuals possibly originated by interspecific cross should be taken into account in the case of seed collection. Our results may contribute to a rationale management of genetic resources of narrow leaved ash, also considering the current legislation on forest reproductive material.